1. Field of the Invention
The present invention is directed to a motor drive circuit. More specifically, the present invention relates to motor drive circuits for bi-directional servo systems.
2. Description of the Prior Art
Conventional pulse width modulated servo systems suffer principally from one of two problems when used as drive servo for reel motors in magnetic tape recorders. Specifically, they are normally single ended i.e., they can only apply drive signal to the reel motor in one direction which limits the size of the tape reels to be used and the rate at which the tape reels can be accelerated. Secondly, prior art pulse width modulated servo systems which are bi-directional have conventionally used a high frequency carrier and varied the pulse width of either the positive or the negative portion of the carrier dependent on the reel motor drive requirements. Thus, the frequency of the carrier changes inversely proportional to the load imposed on the reel motor. This varying frequency can cause severe noise problems in the tape recorder system and can interact with the data frequencies being recorded causing transients which are very difficult to identify and eliminate from the recorded information.